This proposal is in response to PAR-16-330: ?Countermeasures Against Chemical Threats (CounterACT): Identification of Therapeutic Lead Compounds? and incorporates the development of monoclonal antibody (mAb) therapy as a solution for acute exposure to the potent synthetic opioid threat, carfentanil. Beginning in 1979, the illicit synthesis of drugs was elevated to an extraordinarily sophisticated level. A number of overdose victims' deaths were attributed to heroin, however, seized samples contained no heroin, rather the victims were inadvertently buying ?China White? (i.e., ?-methylfentanyl). The fentanyls are a large family of synthetic analgesics that possess all the properties of the opiates, except they are 100-10,000 times more potent than morphine. Reasons for fentanyl resurfacing are tied to a decline in heroin purity, a need to increase potency and cost-efficient preparation. Designer fentanyl's can be synthesized at a single location and because of their potency; a single gram could be formulated (cut) into many thousand, perhaps millions of doses. Preventing the distribution of such small amounts of a pure drug is exceedingly difficult. Thus, while drug control efforts will need to continue, so will efforts to treat synthetic psychoactive drug (SPD) abuse. One (SPD) analogue, carfentanil, is of particular concern because of its extreme potency (10,000 times that of morphine). It has no therapeutic use in humans, posing a significant mortality risk for opioid users. Another issue arises from the persistence of carfentanil in the body; the half-life of the drug exceeds naloxone, requiring multiple infusions of naloxone over time and careful monitoring or else results in re-narcotization. An aerosolized mixture of carfentanil and remifentanil was used as a chemical warfare agent in Russia, resulting in 170 civilian deaths in 2002. A promising therapeutic strategy for attenuating the effects of SPDs can be found in antibody vaccine hapten conjugate. Indeed this strategy has been successfully used against cocaine, nicotine and methamphetamine. Accordingly, we plan to investigate various antibody manifolds stemming from these hapten bioconjugates including catalytic antibodies; importantly each unique antibody manifold may prove more effective than naloxone due drug catabolism and a tunable half-life. We will take two approaches, active and passive vaccine strategies, to counter this dangerous drug, however, both will be grounded upon unique hapten design that will be critical in producing antibodies with tight binding and selective specificity. Antibodies from the latter will come via active vaccination in transgenic OmniRats, and will use a selection process wherein human antibodies will be secured through unique carfentanil-tagged fluorophore coupled with fluorescent-activated cell sorting and analysis. Finally, a metric will be needed to judge the value of both types of vaccines for treating carfentanil's physiological processes; we will look at protection against carfentanil- induced toxicity in both rodents and nonhuman primates. Humanized mAb's against carfentanil will provide a new and improved medical countermeasure to combat the acute toxicity of this chemical threat.